JavaScript绑定方法有什么用

Bind创建一个新函数，该函数将强制函数中的this作为传递给bind()的参数.

下面的示例演示了如何使用bind传递具有正确this的成员方法:

var myButton = {
  content: 'OK',
  click() {
    console.log(this.content + ' clicked');
  }
};

myButton.click();

var looseClick = myButton.click;
looseClick(); // not bound, 'this' is not myButton - it is the globalThis

var boundClick = myButton.click.bind(myButton);
boundClick(); // bound, 'this' is myButton

打印出:

OK clicked
undefined clicked
OK clicked

您还可以在第一个(this)参数之后添加额外的参数，bind会将这些值传递给原始函数.稍后传递给绑定函数的任何附加参数都将在绑定参数之后传入:

// Example showing binding some parameters
var sum = function(a, b) {
  return a + b;
};

var add5 = sum.bind(null, 5);
console.log(add5(10));

打印出:

15

查看JavaScript Function bind了解更多信息和互动示例.

更新:ECMAScript 2015增加了对=>个函数的支持.=>函数更紧凑，并且不会从定义范围更改this指针，因此您可能不需要经常使用bind().例如，如果您希望第一个示例中的Button上的函数将click回调连接到DOM事件，那么以下都是有效的方法:

var myButton = {
  ... // As above
  hookEvent(element) {
    // Use bind() to ensure 'this' is the 'this' inside click()
    element.addEventListener('click', this.click.bind(this));
  }
};

或者:

var myButton = {
  ... // As above
  hookEvent(element) {
    // Use a new variable for 'this' since 'this' inside the function
    // will not be the 'this' inside hookEvent()
    var me = this;
    element.addEventListener('click', function() { me.click() });
  }
};    

或者:

var myButton = {
  ... // As above
  hookEvent(element) {
    // => functions do not change 'this', so you can use it directly
    element.addEventListener('click', () => this.click());
  }
};